Man in the Iron Mask is independent producer Edward Small's 1939 edition of the much-filmed Dumas classic. The title character is the rightful King of France, imprisoned by his pretender-to-the-throne twin brother (both roles are played by Louis Hayward, with an uncredited Peter Cushing doubling for Hayward in the "over the back" shots). Warren William plays musketeer D'Artagnan, who rallies his now aged swashbuckling companions Porthos (Alan Hale), Athos (Bert Roach) and Aramis (Miles Mander), to rescue the real King, whom they have raised from infancy. Director James Whale reserves a juicy cameo part for his old Frankenstein cohort Dwight "Renfield" Frye. Slightly hampered by a limited budget, Man in the Iron Mask was nonetheless popular enough to encourage producer Small to put together another literary derivation in 1940, The Son of Monte Cristo, utilizing many of the same sets.
~ Hal Erickson, All Movie Guide